The long-term goal of this project is to develop a molecular, mechanistic approach to drug targeting. The central hypothesis of this research is: Prodrugs can be targeted to cells over expressing transporters and/or activating (hydrolytic) enzymes to achieve enhanced therapeutic efficacy. The approach utilizes the rapidly advancing knowledge in the areas of genomics, proteomics, and their respective databases, that will greatly facilitate the identification of membrane transporters and activating enzymes responsible for transport and activation of prodrugs. The specific aims of this proposal are: 1: Synthesize a range of aliphatic, aromatic, acidic, basic imino, acidic, and basic, amino acid peptidomimetic prodrugs of floxuridine, gemcitabine and eladribine. 2: Evaluate the prodrugs in vitro for their solution and enzymatic hydrolysis, transport activity and cell growth inhibition activity. 3: Characterize the substrate specificity of BPHL with anticancer prodrugs and correlate with a homology model, produce the enzyme in amounts necessary for structural studies and determine the presence and identity of other prodrug activating enzymes from cancer cells. 4: Correlate the expression levels of transporters and enzymes involved in transport and activation of selected prodrugs in cancer cell lines and correlate with measured transport, prodrug activation and tumor growth inhibition activity. Evaluate two prodrug candidates in vivo for each parent drug for targeting potential and correlation with in vitro activity. This proposal will take advantage of the broad specificity of hPEPT1 (and other transporters) for nucleoside analogue prodrugs, and of our very exciting recent finding of an enzyme, valacyclovir hydrolase (BPHL), that activates the prodrugs valcyclovir and valganciclovir. We will develop and apply a molecular mechanistic approach to drug targeting, based on these findings and test this strategy in vivo with prodrugs of known anticancer agents. These studies will develop molecular mechanistic approaches for targeting anticancer prodrugs. The targeting approach and methods as well as structure-activity correlations developed in this project will be broadly applicable to the development of targeting strategies for other disease states and would be of immense value in optimizing drug discovery and development processes.